Surface temperature probes are known in the art. Contacting-type surface temperature probes are designed to be brought into contact with a surface in order to measure the temperature of the surface. For example, U.S. Pat. No. 4,859,081 describes a surface temperature probe which includes a thin plate spring with a thermocouple junction on a central portion thereof. The plate spring is fixed at both its ends to a support member so that the plate spring projects semicircularly in side elevation to form a temperature sensing portion. The semicircular plate spring and thermocouple junction are brought into contact with the surface to be measured and are pressed lightly against the surface to flatten slightly the semicircular portion of the plate spring. As a result, part of the plate spring and the thermocouple junction are engaged closely in press contact with the surface to be measured.
U.S. Pat. No. 4,279,154 describes a similar probe which utilizes a pair of foil strips of thermocouple materials which are butted or partly overlapped at their one ends to form a thermocouple junction thereat. The foil strips are overlaid across a plate spring including resilient support strips which provide contact pressure relative to the surface to be measured.
There are several drawbacks associated with conventional contact-type surface temperature probes. For example, FIG. 8a of the present application shows a conventional lap joint 1 formed between two thermocouple materials 2 on a resilient support strip 4. The lap joint 1 forms the thermocouple junction 5 which is to be engaged in press contact with the surface to be measured. The lap joint 1 results in a non-uniformity 6 in the thermocouple junction which prevents the thermocouple junction 5 from engaging uniformly in press contact with the surface to be measured, thereby introducing measurement error.
FIG. 8b of the present application illustrates a thermocouple junction 5' formed using a conventional butt joint 8 between the end surfaces of the thermocouple materials 2. The butt joint 8 is typically formed using a butt welder, for example, whereby the end surfaces of the thermocouple materials 2 are welded together. A problem arises however in that the end surfaces of the thermocouple materials typically have a very small surface area, e.g., on the order of four thousandths of an inch by one sixteenth of an inch. During welding of the butt joint 8, sputtering, flash, etc. can occur, thereby producing undesirable buildup at the joint 8. For example, a non-uniformity such as a burr 10 or the like may form on the surface of the butt joint 8. The burr 10 can prevent the thermocouple junction 5' from engaging in proper uniform contact with the surface to be measured, again introducing measurement error. As a result, another manufacturing step is necessary in order to remove the burr 10. Thus, additional manufacturing time and expense is necessary.
Still another drawback associated with conventional surface temperature probes is the use of an electrical insulating layer between the thermocouple materials and the spring plate. In the past, surface temperature probes have included a ceramic insulating layer approximately 20 microns thick between the thermocouple materials and the spring plate. Unfortunately, the ceramic layer can exhibit the normal brittle bulk properties associated with ceramic. This results in a probe tip which is likely to have reduced flexibility and thus be susceptible to damage due to, for example, the plate spring becoming overflexed and the ceramic layer breaking.
Yet another problem associated with conventional surface temperature probes is inadequate protection against overtravel of the thermocouple junction and spring plate. For example, a user may apply too much force applying the probe to the surface to be measured. As a result, the spring plate may flatten too far so as to permanently bend and/or break the plate spring or thermocouple junction. Conventional probes such as that described in the above-mentioned '081 patent attempt to overcome such a problem by including semicircular housing walls which substantially encircle the resilient contact surface. The housing walls limit the distance the spring plate and thermocouple junction can be deflected when pressed against a surface. However, such housing walls are not effective in the event surfaces are contacted which are smaller than the diameter of the housing walls, as in the case of screw heads, etc., or if the plate spring is pushed with a finger, etc. As a result, conventional surface temperature probes are still subject to damage due to overtravel of the spring plate, etc.
Still another drawback of conventional surface temperature probes relates to the thermal properties of the spring plate. A spring plate which is generally solid has a relatively high thermal mass which can adversely affect temperature measurements. As an alterative, the above-mentioned '154 patent describes a probe which uses a spring plate consisting of a pair of relatively thin resilient strips having cross members therebetween. The thermocouple materials are positioned across the cross members. The spring plate tends to have a lower thermal mass. However, such a spring plate does not ensure as large a contact area as the solid spring plate to ensure good contact between the thermocouple junction and the surface being measured. The cross members provide support to the thermocouple junction only in small, localized areas.
In view of the aforementioned shortcomings associated with conventional contact-type surface temperature probes, there is a need in the art for a surface temperature probe and a method of making such having a uniform thermocouple junction, particularly without requiring additional processing steps to remove non-uniformities. Moreover, there is a need in the art for a surface temperature probe having a ceramic insulating layer which does not exhibit the normal brittle bulk properties of ceramic. There is also a need for a surface temperature probe which includes means for preventing overtravel of the spring plate and/or thermocouple junction, even in the event of contact with a relatively small surface. Finally, there is a need for a spring plate for a surface temperature probe which provides support for a large contact area while still having a low degree of thermal mass.